1. Field of the Invention
The present disclosure relates to a sheet feeding apparatus capable of separating sheets to feed thus separated sheets one by one and an image forming apparatus equipped with the sheet feeding apparatus.
2. Description of the Related Art
Generally, in an image forming apparatus such as a printer, a facsimile, and a copying machine, a body of the image forming apparatus includes integrally or detachably a sheet feeding apparatus for automatically feeding a recording material such as plain paper, coated paper, and an overhead projector (OHP) sheet (hereinafter simply referred to as “sheet”) to an image forming unit of the image forming apparatus. The sheet feeding apparatus is equipped with a separation feeding unit for separating sheets to feed thus separated sheets one by one to an image forming unit. The image forming unit forms an image on the sheet having been separated and fed one by one from the sheet feeding apparatus. Therefore, in the sheet feeding apparatus, it is one of challenges to separate the sheets and feed the separated sheet to the image forming unit continuously one by one. Accordingly, various feeding methods are proposed to prevent double feeding in which a plurality of sheets is conveyed at a time.
Lately, more downsizing of the image forming apparatus is demanded due to a wide spread of the image forming apparatus into typical households. Therefore, in the image forming apparatus equipped with the sheet feeding apparatus including a sheet stack tray on which sheets are stacked, it is demanded that a length of the apparatus body in a sheet feeding direction (e.g., a depth) would not be longer than a length of the sheet stack tray in the sheet feeding direction. To meet the above described demand, proposed is an image forming apparatus in which a sheet is conveyed in a direction opposite to the sheet feeding direction and the sheet is once flexed by bringing the sheet into contact with a trailing edge wall of the sheet stack tray, followed by running-on of a sheet over a separation claw and by separating and conveying the sheet by means of the separation claw, resulting in separation feeding of the sheets within the sheet stack tray of the current size. The above described technique is discussed in Japanese Patent Application Laid-Open No. 05-147752.
These days, in addition to the above descried demand of downsizing of the image forming apparatus, another challenge is to steadily feed various types of sheets having different thicknesses. More specifically, a problem to solve is how to steadily feed a sheet having less rigidity (e.g., a thin paper). To solve the above described problem, such an image forming apparatus is proposed that the sheets are stacked on the sheet stack tray in a manner such that the sheets are curled in a direction orthogonal to the sheet feeding direction, thereby enhancing apparent rigidity of the sheets in the sheet feeding direction and the thin papers are properly dealt with on a surface of a slope, resulting in preventing double feed of the thin papers. The technique is discussed in Japanese Patent Application Laid-Open No. 2000-143002.
However, the image forming apparatus discussed in Japanese Patent Application Laid-Open No. 05-147752 requires a space for causing the sheets to be flexed and thus the downsizing of the image forming apparatus is hard to achieve. On the other hand, the image forming apparatus discussed in Japanese Patent Application Laid-Open No. 2000-143002 requires no space for causing the sheets to be flexed; however, since the sheets are stacked in a curved condition for a long period of time in such image forming apparatus, the sheets are curled and fixed in a curling shape, which may invite a faulty conveyance such as a sheet jam while the sheets are fed, and further which may invite a faulty transfer of an image while the images are transferred to the sheets. If after the images are formed and discharged, the sheets are curled and fixed in the curling shape, quality of the sheets as printed matters is degraded.